I've found a perfect solution to the half length mounts for a boot device for the raspi.

Norcent microSD Trio Memory Card w/USB/SD Adapter

 

If you notice, it has a perfect half-length microSD adapter with a usb 'tail' which can be safely removed, leaving us with only a tidy half-length SD adapter.  Now the only problem is finding one, as they seem to be sold out everywhere.

Once I get my hands on one I'll document my modifications.